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Hi Graeme, free reflections are used for two purposes, at least: cross-validation (calculation of Rfree) and ML parameters estimation (sigmaa or alpha/beta). For the latter it is important that each relatively thin resolution bin (sufficiently thin so that alpha/beta can be considered constants in it) receives no less than 50 reflections absolute min; in Phenix we found that ~150 per bin is sufficient and this is what's used by default. Pavel On Tue, Jun 2, 2015 at 3:26 AM, Graeme Winter <[log in to unmask]> wrote: > Hi Folks > > Had a vague comment handed my way that "xia2 assigns too many free > reflections" - I have a feeling that by default it makes a free set of 5% > which was OK back in the day (like I/sig(I) = 2 was OK) but maybe seems > excessive now. > > This was particularly in the case of high resolution data where you have a > lot of reflections, so 5% could be several thousand which would be more > than you need to just check Rfree seems OK. > > Since I really don't know what is the right # reflections to assign to a > free set thought I would ask here - what do you think? Essentially I need > to assign a minimum %age or minimum # - the lower of the two presumably? > > Any comments welcome! > > Thanks & best wishes Graeme >